There is known an acoustic wave device equipped with an interdigital electrode and a pad electrode on a piezoelectric substrate, as the acoustic wave device using an acoustic wave. The acoustic wave device is used for a bandpass filter and a duplexer in a mobile communication terminal represented by a cellular phone. Recently, low loss of a filter is desired due to the improvement of a reception sensitivity, the reduction of a power consumption and so on of the mobile communication terminal. Factors of an insertion loss include, for example, a propagation loss of the acoustic wave, a leakage of the acoustic wave from a waveguide, a resistance loss of the interdigital electrode, a resistance loss in wiring and the pad electrode, and so on.
In general, the interdigital electrode is made of aluminum (Al) having a small electric resistance and a small density, or an alloy of aluminum. However, using materials other than aluminum and laminating different materials are proposed in view of power durability, characteristics or the like (e.g. see Japanese Patent Application Publication Nos. 7-122961, 2007-251710 and 2003-209458, and Masakazu Mimura et al., “Improvement Technique in Temperature Characteristics of Boundary Acoustic Wave Resonators using Multi-layered Electrodes”, Proceedings of Symposium on Ultrasonic Electronics, 2011, vol. 32, pp. 213-214).
Generally, the pad electrode, and the wiring connecting the pad electrode and the interdigital electrode are formed simultaneously with the interdigital electrode in view of the simplification of a manufacturing process. In addition, there is a proposal for making the thickness of the wiring thicker than the interdigital electrode in order to reduce an electric resistance of the wiring (e.g. see Japanese Patent Application Publication No. 2010-252321).
Japanese Patent Application Publication No. 2010-252321 proposes reducing the electric resistance by making the wiring thick, but does not take an electric resistance of the pad electrode in a direction perpendicular to the piezoelectric substrate into consideration.